The aging of society in recent years is accompanied by the increase in the number of patients with developed diseases (for example, Parkinson disease, and paralysis, epilepsy) caused by brain disorder. Clarification of brain functions, in particular clarification of nerve circuit activity inside the brain is an indispensible means for developing methods for treating the diseases caused by brain disorder. Brain probes that are inserted into the brain to detect electric signals (brain waves) of brain cells have been used for such purpose. Furthermore, the brain probes can be also used as a means for supplying electric stimulation into the brain in order to specify the location in which the brain disorder has occurred in the treatment of diseases caused by brain disorder.
Further, in recent years, brain probes have also found use as medical tools providing electric stimulation to restore the brain functions, and clinical tests have also been conducted on humans as part of the BMI (Brain-Machine Interface) or BCI (Brain-Computer Interface) research.
BMI is a system with indirect brain-machine interaction and can be generally classified into motion-type BMI, sensation-type BMI, and direct operation BMI. The motion-type BMI is a technique for detecting and using the activity representing the motion output, from among various types of neural activity of the brain, and controlling an external device such as a robot. Such a technique is used, for example, for motion function rehabilitation in quadriplegic patients. The sensation-type BMI is a technique for transmitting signals into the brain and inducing and enhancing various sensations. Some of the sensation-type BMI have already found practical use, representative examples thereof including artificial inner ear and artificial retina. The direct operation BMI is a technique for restoring various damaged functions by direct stimulation inside the brain.
The BCI is a general term for an interface that directly connects electric signals flowing inside the human brain with a computer, thereby making it possible to operate the computer by thoughts. The BCI includes a technique by which brain wave signals are read on the head surface by using a hat-like electrode, and a technique by which an electrode is directly inserted into the brain and neuron activity is read as signals.
A variety of drug treatment methods are used for treating the Parkinson disease, but the effect of the drug treatment methods is lost after a long time and side effects are sometimes demonstrated. With respect to patients for whom the drug treatment is ineffective, DBS (Deep Brain Stimulation) for stimulating the cerebrum basal ganglia becomes a treatment of choice.
In a brain probe that is inserted into the brain for detecting electric signals inside the brain and providing electric stimulation to the brain, for example, as disclosed in the below-described Non-Patent Document 1, an electrode is disposed on a tip of a fine probe made of silicon and having a diameter of about several hundreds of microns by using a LSI (Large Scale Integration) manufacturing technique, and the electrode is connected by a lead-out wiring to a bonding pad on the other end side for connection to an external device. Further, the brain probe suggested in Non-Patent Document 1 is configured to have a length (above 40 mm) sufficient to reach the basal ganglia in the deep portions of cerebrum and have electrodes on both planes, rather than one plane, of the tip portion thereof. By disposing the electrodes on both planes, it is possible to detect electric signals from both sides of the brain probe.
Non-Patent Document 1: Japanese Journal of Applied Physics 48 (2009) 04C194.
However, the brain probe described in Non-Patent Document 1 has the following drawbacks. Thus, since the entire brain probe described in Non-Patent Document 1 is formed from a silicon substrate, the brain probe is brittle and cannot be inserted individually when inserted deeply into the brain, for example, to the basal ganglia. The brain probe described in Non-Patent Document 1 is guided into the brain by additionally using a metal tube, inserting the metal tube into the brain, and then inserting the brain probe described in Non-Patent Document 1 into the metal tube.
Further, since the brain probe of the Non-Patent Document 1 is oriented by the frontal direction (normal direction) of the planes (front plane, rear plane), the electric signal from the frontal direction is received with better sensitivity than the electric signal from the horizontal direction and sufficient reception sensitivity cannot be obtained for the entire circumference of the brain probe. Thus, the problem is that although the electrodes are disposed on both surfaces, electric signals from specific directions cannot be received with sufficient sensitivity.